Extinctions

This living world has had its times of stress. It is interesting that one of the significant events in Greek philosophy was the recognition that the world was not static, but constantly was changing. There have been several times in history where major changes occurred with loss of life, species and the creation of new directions in life.
Here is a timeline with markings where major extinction events occurred:

• the end of the Tertiary Period, 1.6 million years (m.y.) ago.
• the end of the Cretaceous Period, marking the boundary between the Cretaceous and Tertiary periods 65 m.y. ago. (Geologists use the letter K to stand for Cretaceous Period and the letter T for the Tertiary Period. Thus this boundary is commonly called the K-T boundary): Dinosaurs. Believed from a drop in seas and a massive asteroid that hit the Yucatan Peninsula.
• the end of the Triassic, 208 m.y. ago. No explanation but countless theories.
• the end of the Permian, 245 m.y. ago (estimated that over 96% of the species alive at the time became extinct). All of current species descended from that 4%. Cause unknown.
• the end of the Devonian, 360 m.y. ago
• the end of Ordovician, 438 m.y.: ago 85% of sea life
• the end of the Cambrian period, 505 m.y. ago